GB2577073A

GB2577073A - Characterisation method and apparatus

Info

Publication number: GB2577073A
Application number: GB1814829.6A
Authority: GB
Inventors: Fu Richard; Torun Hamdi
Original assignee: Of Northumbria At Newcastle, University of; Northumbria University
Current assignee: Of Northumbria At Newcastle, University of; Northumbria University
Priority date: 2018-09-12
Filing date: 2018-09-12
Publication date: 2020-03-18
Also published as: WO2020053561A1; GB201814829D0

Abstract

Electrical resonator device 101 comprises interdigitated transducer (IDT) 102 coupled with the medium (e.g. a fluid). The device is stimulated with electromagnetic (EM) energy, establishing a circulating current, at a frequency dependent on capacitance of the IDT, within the device. The frequency is detected and used to characterise the medium (e.g. fluidic loading). The EM energy may be emitted by an antenna – perhaps a loop antenna, perhaps encircling the device – proximate to the device. The frequency may be detected from a change in absorption of EM energy by the device, perhaps by measuring attenuation of the EM energy using a second proximate antenna. The device may be a surface acoustic wave (SAW) device, having electrodes coupled to the two sets of fingers of the IDT and separated by a gap. The SAW device may actuate the medium. Multiple such devices may detect multiple frequencies in multiple media.

Description

(71) Applicant(s):

University of Northumbria at Newcastle Sutherland Building, College Street, Newcastle, upon Tyne, NE1 8ST, United Kingdom (72) Inventor(s):

Richard Fu

Hamdi Torun (74) Agent and/or Address for Service:

Definition IP Limited

The Core, Science Central, Bath Lane, NEWCASTLE UPON TYNE, Tyne & Wear, NE4 5TF, United Kingdom (51) INT CL:

G01N 27/22 (2006.01) G01N 29/02 (2006.01) (56) Documents Cited:

EP 3086116 A1 US 7038470 B1

US 20160187280 A1 (58) Field of Search:

INT CL G01N

Other: EPODOC, WPI, Patent Fulltext, XPESP, SPRINGER, XPAIP, XPIOP (54) Title of the Invention: Characterisation method and apparatus

Abstract Title: Characterising a medium using an interdigitated transducer (57) Electrical resonator device 101 comprises interdigitated transducer (IDT) 102 coupled with the medium (e.g. a fluid). The device is stimulated with electromagnetic (EM) energy, establishing a circulating current, at a frequency dependent on capacitance of the IDT, within the device. The frequency is detected and used to characterise the medium (e.g. fluidic loading). The EM energy may be emitted by an antenna - perhaps a loop antenna, perhaps encircling the device - proximate to the device. The frequency may be detected from a change in absorption of EM energy by the device, perhaps by measuring attenuation of the EM energy using a second proximate antenna. The device may be a surface acoustic wave (SAW) device, having electrodes coupled to the two sets of fingers of the IDT and separated by a gap. The SAW device may actuate the medium. Multiple such devices may detect multiple frequencies in multiple media.

105

Amplitude of output signal

Resonant frequency

FIG. 1

Freq /8

105

frequency

FIG. 1

2/8

C|DT

L₁ electrode ( j l_₂ electrode r

'“'GAP

FIG. 2

FIG. 3a

3/8

S101

S102

S103

S104

FIG. 4

4/8

Cr/Au: 50nm/120nm

I \ A \ \ A \ ^; \ A \ A A ^Zn0:

Ni: 25μΓΠ

FIG. 5b

5/8

6/8

105

7/8

701a

703a

12 19

703b

701b j

FIG. 7

8/8

12 19

105

FIG. 8

CHARACTERISATION METHOD AND APPARATUS

Technical Field

The present invention relates to a technique for characterising mediums, such as 5 fluids.

Background

Techniques for analysing and characterising matter, such as fluids, and in particular biological fluids, are increasingly important and widely used. Demand for such 10 analysing techniques, and in particular techniques for characterising fluid composition and constituent composition is driven at least in part by recent advances in microfluidic technology that allow increasingly complex assays relating to molecular biology analysis to be performed.

However, conventional techniques are typically complicated and require specific devices and techniques to be employed to perform different types of characterising operations.

Summary of the Invention

In accordance with a first aspect of the invention, there is provided a method of characterising a medium. The method comprises: stimulating with electromagnetic energy at least one electrical resonator device comprising an interdigitated transducer, said interdigitated transducer coupled with the medium; detecting a frequency of the electromagnetic energy at which the electromagnetic energy establishes a circulating current within the electrical resonator device, said frequency dependent on a capacitance of the interdigitated transducer device, and characterising the medium based on the detected frequency.

Optionally, stimulating the device with electromagnetic energy comprises emitting electromagnetic energy from a first antenna proximate the electrical resonator device.

Optionally, the frequency of the electromagnetic energy at which the circulating current is established in the electrical resonator device is detected by detecting a change in the absorption of the electromagnetic energy by the electrical resonator device.

Optionally, the method further comprises receiving electromagnetic energy emitted from the first antenna at a second antenna proximate the interdigitated transducer device, and measuring an attenuation of the received electromagnetic energy emitted from the first antenna to detect the absorption of the electromagnetic energy by the interdigitated transducer.

Optionally, the electrical resonator device is positioned substantially between the first antenna and second antenna.

Optionally, the first antenna is coupled to an oscillator.

Optionally, the first antenna is a loop antenna.

Optionally, the loop antenna substantially encircles at least part of the electrical resonator device.

Optionally, the method further comprises measuring a reflection parameter of the electromagnetic radiation at the loop antenna to detect the absorption of the electromagnetic energy by the electrical resonator device and thereby determine the frequency at which the electromagnetic energy establishes the circulating current within the electrical resonator device.

Optionally, the method further comprises stimulating with the electromagnetic energy one or more further electrical resonator devices each further electrical resonator device comprising a further interdigitated transducer each interdigitated transducer coupled with a further medium, detecting one or more further frequencies of the electromagnetic energy at which the electromagnetic energy establishes circulating currents within the one or more further electrical resonator devices, said one or more further frequencies dependent on a capacitance of the one or more further interdigitated transducer devices, and characterising the one or more further mediums based on the one further detected frequencies.

Optionally, the frequency and the one or more further frequencies are detected substantially contemporaneously.

Optionally, the electrical resonator device comprises a surface acoustic wave (SAW) device.

Optionally, the interdigitated transducer comprising a first set of fingers and a second set of fingers, said first and second set of fingers interdigitated with each other.

Optionally, the surface acoustic wave device comprises a first electrode electrically coupled to the first set of fingers and a second electrode coupled to the second set of fingers.

Optionally, the first electrode and second electrode are separated by a gap.

Optionally, the method further comprises applying electrical energy to the surface acoustic wave device to actuate the medium.

Optionally, the medium is a fluid.

Optionally, the capacitance of the interdigitated transducer is dependent on a fluidic loading of the fluid on the interdigitated transducer.

In accordance with a second aspect of the invention, there is provided an apparatus for characterising a medium. The apparatus comprises at least one electrical resonator device comprising an interdigitated transducer. The interdigitated transducer is operable to be coupled to the medium to be characterised. The apparatus further comprises an electromagnetic energy emitter operable to stimulate the electrical resonator device with electromagnetic energy and a detector operable to detect a frequency of the electromagnetic energy at which the electromagnetic energy establishes a circulating current within the electrical resonator device, said frequency dependent on a capacitance of the interdigitated transducer device, said detected frequency enabling the medium to be characterised.

Optionally, the electromagnetic energy emitter comprises a first antenna proximate to the electrical resonator device.

Optionally, the detector is arranged to establish the frequency of the electromagnetic energy at which the circulating current is established in the electrical resonator device is detected by detecting a change in the absorption of the electromagnetic energy by the electrical resonator device

Optionally, the detector further comprises a second antenna proximate to the electrical resonator device operable to receive electromagnetic energy emitted from the first antenna, said detector comprising a signal analyser operable to measure an attenuation of the received electromagnetic energy emitted from the first antenna to detect the absorption of the electromagnetic energy by the interdigitated transducer.

Optionally, the first antenna is coupled to an oscillator.

Optionally, the first antenna is a loop antenna.

Optionally, the loop antenna is connected to a vector network analyser operable to measure a reflection parameter of the electromagnetic radiation at the loop antenna to detect the absorption of the electromagnetic energy by the electrical resonator device and thereby determine the frequency at which the electromagnetic energy establishes the circulating current within the electrical resonator device.

Optionally, the apparatus further comprises at least one or more further electrical resonator devices comprising interdigitated transducers, the interdigitated transducers of the further electrical resonator device each operable to be coupled to further mediums to be characterised, wherein the electromagnetic energy emitter is operable to stimulate the one or more further electrical resonator devices with electromagnetic energy and the detector is operable to detect one or more further frequencies of the electromagnetic energy at which the electromagnetic energy establishes circulating currents within the one or more further electrical resonator devices, said one or more further frequencies dependent on a capacitance of the one or more interdigitated transducer device, said detected frequencies enabling the one or more further mediums to be characterised.

Optionally, the detector is operable to detect the one or more further frequencies substantially contemporaneously.

Optionally, the first electrode and second electrode are separated by a gap.

Optionally, the apparatus further comprises a power source for applying electrical energy to the surface acoustic wave device to actuate the medium.

Optionally, the medium is a fluid.

In accordance with aspects of the invention, a technique is provided which allows mediums, such as fluids, to be characterised. Unlike conventional techniques, the characterisation is based on the detection of a resonant frequency of an electrical resonator device which includes an interdigitated transducer (IDT) array. The resonant frequency of such a device is strongly dependent on the capacitive properties of the IDT (arising due to the gaps between the set of fingers of the array). This means that small changes in the capacitance of the IDT are readily observed in changes in the resonant frequency of the electrical resonator device. When the IDT is coupled to (for example in contact with and/or capacitively coupled with) mediums properties of the medium give rise to changes in the capacitance of the IDT. Accordingly, mediums can be readily characterised by observing relative changes in the resonant frequency of the electrical resonator device brought about when they are coupled with the IDT.

In certain embodiments, the electrical resonator device is stimulated by electromagnetic radiation from a first antenna proximate to the electrical resonator device and the resonant frequency of the electrical resonator device is determined by detecting an attenuation of electromagnetic energy emitted from the first antenna incident on a second antenna proximate the electrical resonator device. Advantageously, this enables a medium to be characterised wirelessly. That is, the electrical resonator device can be a passive component.

Advantageously, in certain embodiments, the electrical resonator device can be provided by a conventional surface acoustic wave (SAW) device.

Advantageously, in such embodiments, the SAW device can be used to actuate stimulate the medium.

Typically, particularly when processing mediums such as biological fluids, the steps of actuating/stimulating the fluids is separate to the step of analysing the fluids and usually requires separate actuation means and analysing means to be provided. Advantageously, in accordance with certain embodiments of the invention, this can be provided by a single arrangement and, in certain examples, both steps can be undertaken simultaneously.

Various further features and aspects of the invention are defined in the claims.

Brief Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings where like parts are provided with corresponding reference numerals and in which:

Figure 1 provides a simplified schematic diagram of a modified surface acoustic wave (SAW) device arranged in accordance with certain embodiments of the invention;

Figure 2 provides a schematic diagram of an equivalent electrical model of the SAW device shown in Figure 1;

Figures 3a and 3b provide simplified schematic diagrams of a SAW device in accordance with certain embodiments of the invention, with Figure 3b showing the SAW device with a sample-holding cell;

Figure 4 provides a schematic diagram of a process for characterising a medium in accordance with certain embodiments of the invention;

Figure 5a provides a schematic diagram of a SAW device in accordance with certain embodiments, showing in particular a number of illustrative dimensions of the device;

Figure 5b provides a schematic diagram of a cross-sectional view of a SAW device in accordance with certain embodiments of the invention;

Figure 6a provides a schematic diagram of a SAW device in accordance with certain embodiments of the invention in which a loop antenna is provided;

Figure 6b provides a schematic diagram of a SAW device in accordance with certain embodiments of the invention;

Figure 7 provides a schematic diagram of an array of two SAW devices in accordance with certain embodiments of the invention, and

Figure 8 provides a schematic diagram of an apparatus in accordance with certain embodiments of the invention including a power source for providing electrical energy to a SAW device for actuating a medium.

Detailed Description

Figure 1 provides a simplified schematic diagram of an apparatus for conducting a characterising process in accordance with certain embodiments of the invention. The apparatus includes an electrical resonator device provided by a surface acoustic wave (SAW) device 101.

The SAW device 101 includes an interdigitated transducer (IDT) array 102. The IDT 102 comprises a first and second set of interdigitated “fingers”. A first set of fingers of the IDT 102 are connected to a first electrode 103 and a second set of fingers of the IDT 102 are connected to a second electrode 104. The apparatus further includes an antenna pair 105 comprising a first antenna 105a and a second antenna 105b. The SAW device 101 is positioned between the first antenna 105a and second antenna 105b. Each antenna of the antenna pair 105 can be provided by a suitable antenna arrangement such as a monopole patch antenna.

The apparatus further comprises an RF (Radio Frequency) oscillator 106 and an amplifier 107.

The first antenna 105a is connected to the RF oscillator 106 which provides an oscillating current. Together, the first antenna 105a and the RF oscillator 106 provide an electromagnetic energy emitter operable to stimulate the electrical resonator device with electromagnetic energy.

This oscillating current is supplied to the first antenna 105a of the antenna pair 105 which causes the first antenna 105a to emit electromagnetic energy. This electromagnetic energy is incident on the second antenna 105b. The second antenna 105b absorbs some of the radiated energy from the first antenna.

The second antenna 105b is connected to the amplifier 107 which is arranged to amplify electromagnetic energy absorbed by the second antenna 105b and generate an output signal indicative of the strength of the electromagnetic energy absorbed by the second antenna. The oscillator 106 and the amplifier 107 are typically linked so that the amplifier can be “tuned”, with appropriate circuitry as is well-known in the art, to amplify frequencies received by the second antenna 105b that are being emitted by the first antenna 105a

Typically, the amplitude of the output signal corresponds with the strength of the received electromagnetic energy. The output signal is typically input to a signal analyser. 108. Together, the second antenna 105b and the amplifier 107 provide a detector operable to detect the frequency of the electromagnetic energy at the circulating current within the electrical resonator device is stimulated.

When stimulated by electromagnetic energy at a resonant frequency, a circulating current is established within the SAW device 101, i.e. through the IDT 102, the first electrode 103 and the second electrode 104.

As the frequency of the radiated electromagnetic energy is changed, the amount of electromagnetic energy absorbed by the second antenna 105b remains constant apart from at the resonant frequency of the SAW device 101 where the amount of energy absorbed by the second antenna 105b reduces. This is because, at the resonant frequency, some of the energy from the electromagnetic energy is absorbed by the SAW device 101 and the circulating current is established.

Accordingly, as the frequency of the radiated electromagnetic energy is changed (by changing the frequency of the oscillating current provided by the oscillator 106) the amplitude of the output signal from the amplifier 107 is substantially constant apart from at the resonant frequency where a reduction is observed. This is depicted in the graph shown in Figure 1. The resonant frequency (i.e. the frequency at which the electromagnetic energy is absorbed by the SAW device 101) can be detected by the signal analyser 108 from the output signal from the amplifier 106.

The resonant frequency is determined by electrical parameters of the SAW device 101 which forms an electrical resonator device (e.g. a resonant circuit sometimes referred to as an “LC resonator”). These electrical parameters are depicted in Figure

2.

Figure 2 provides a schematic diagram of an equivalent electrical model of the electrical resonator device formed by the SAW device 101 shown in Figure 1.

The circuit comprises a first capacitance (Cidt) associated with the IDT 102 in series with a first inductance (Li electrode) associated with the first electrode 103 which is in series with a second capacitance (C_gap) associated with the gap between the first electrode 103 and the second electrode 104. The second capacitance (C_gap) is in series with a second inductance (l_2 electrode) associated with the second electrode 104 which, in turn, is in series with the first capacitance (Cidt).

The electrical parameters, shown in Figure 2 are dependent on the physical properties of the SAW device 101 including the physical geometry (e.g. size and shape) of the IDT, the electrodes and the gap between the electrodes.

In particular, the resonant frequency of the SAW device 101 is dependent on Cidt which is determined by the geometry of the IDT 102. The resonant frequency of the SAW device is typically strongly dependent on Cidt with a quality factor of a typical IDT being around 1000 at microwave frequencies.

Accordingly, small changes in Cidt change the resonant frequency of the SAW device 101. Various factors will change the value of Cidt, in particular, certain characteristics of any medium coupled with the IDT. Accordingly, the apparatus provides a means to characterise medium bought into contact with the IDT

For example, if a medium, such as a fluid is brought into close proximity or direct contact with the IDT, it will capacitively couple with the IDT thereby altering Cidt. Different quantities and different densities of fluid will cause different changes in Cidt therefore the apparatus can be used to detect, for example, the fluidic loading at the IDT.

Therefore, advantageously, tracking the resonant frequency of SAW device 101 provides a means to characterise mediums (for example fluids) to which the IDT 102 of the SAW device is coupled.

Thus, in accordance with certain embodiments of the invention, apparatus of the type described with reference to Figures 1 and 2 can be used in a characterising process for characterising various mediums, for example fluids.

Figure 3a provides a simplified schematic diagram of a characterising device 301 in accordance with certain embodiments of the invention. The characterising device 301 includes a SAW device which comprises an IDT 302, a first electrode 303, a second electrode 304 and an antenna pair comprising a first transmission antenna 305 connected via port 305a to an oscillator (not shown) and a second reception antenna 306 connected via a port 306a to an amplifier for generating an output signal (not shown).

Figure 3b provides a simplified diagram of the characterising device 301 described with reference to Figure 3a and further shows a sample-holding cell 307. The sample-holding cell 307 is positioned over at least part of the IDT of the SAW device. The sample-holding cell contains a medium, such as a fluid, to be characterised. Typically, the sample-holding cell is arranged so that the medium to be characterised is either in direct contact with the IDT or within a vicinity of the IDT to enable the fluid and the IDT to capacitively couple.

In certain embodiments, optimum location of the medium relative to the IDT is determined to maximise capacitive coupling between the IDTs and fluid and the sample-holding cell arranged accordingly.

As mentioned above, the resonant frequency of the SAW device changes in dependence on the capacitance Cidt of the IDT in the resonating circuit formed by components of the SAW device (i.e. IDT, electrodes and the gap between the electrodes). Accordingly, by detecting the resonant frequency of the SAW device, the medium in the sample-holding cell can be characterised.

For example, it may be desirable to determine whether a first fluid sample is the same (e.g. contains the same constituents in the same concentrations) as a second fluid sample.

In accordance with such an example, a sample of the first fluid is characterised.

Specifically, the first fluid is positioned in the sample-holding cell 307 of the characterising device 301 and the ports 305a and 306a of the characterising device are connected respectively to an oscillator and amplifier thus forming an apparatus of the type described with reference to Figure 1. Typically, the output signal from the amplifier is input to a signal analyser as described above and the resonant frequency of the SAW device in this configuration is measured by determining the frequency of the electromagnetic radiation at which the output signal dips.

The signal processing analyser can be provided by any suitable signal processor known in the art. The signal processing unit can be arranged to perform suitable signal processing functions such as frequency spectral analysis or frequency counting to identify the frequency at which the dip occurs.

Subsequently, the same process is performed for the second fluid sample. If the resonant frequency determined when the second sample is positioned in the sampleholding cell is the same as the resonant frequency determined when the first sample is positioned in the sample-holding cell, it can be inferred that the first and second samples are the same and thus the second sample includes the cells of the certain type. This is because, for the resonant frequency to be the same, the value of Cidt must be the same and this will only be the case if the capacitive coupling with the IDT is the same thus indicating that the first sample and second sample are the same.

On the other hand, if the resonant frequency determined when the second sample is positioned in the sample-holding cell is different from the resonant frequency determined when the first sample is positioned in the sample-holding cell, it can be inferred that the first and second samples are different. This is because, if the resonant frequency is different, the value of Cidt must be different and this indicates that the capacitive coupling is different and assuming all other factors are equal, the fluidic loading will only differ if the first sample and second sample are different.

Typically, information about fluid loading can be inferred from the shift in the resonant frequency. Thus, for example, the magnitude of shift can be used to further characterise the fluid by assessing an amount of detected analyte. Furthermore, in certain examples, the direction of shift is indicative of the relative magnitude of the electromagnetic permittivity of the fluid. The fluid can thus be further characterised by determining properties related to its permittivity. Thus, for example, a detected decrease in resonant frequency indicates that the second sample in the sampleholding cell comprises an analyte with a lower permittivity.

Figure 4 provides a flow diagram depicting a process for performing a characterisation method in accordance with certain embodiments of the invention.

At a first step S101, a medium to be characterised, for example a fluid, is coupled to an interdigitated transducer array which is part of an electrical resonator device.

At a second step S102, the electrical resonator device is stimulated with electromagnetic energy, for example from an antenna which is proximate to the electrical resonator device.

At a third step S103 the resonant frequency of the electrical resonator device is determined. That is, the frequency of the electromagnetic energy at which a circulating current is stimulated within the electrical resonator device. This can be achieved, for example, by measuring a strength of the electromagnetic energy incident on a second antenna proximate the electrical resonator device to identify the frequency at which this energy drops below a level observed for other frequencies.

At a fourth step, the medium is characterised based on the detected frequency. This characterisation can be achieved, for example as described above, by comparing the detected frequency with the previously detected frequency for a medium which has known characteristics.

Figure 5a provides a simplified schematic diagram of a SAW device in accordance with certain embodiments of the invention, showing in particular, exemplary dimensions of the device. As can be seen from Figure 5a, in certain embodiments, the length of each electrode is approximately 15mm; the width of the IDT is approximately 10mm; the length of the IDT (i.e. in the direction of the electrodes) is approximately 9mm; the gap separating the electrodes is approximately 4mm and each electrode has a base pad measuring approximately 3mm by 4mm.

Figure 5b provides a cross-sectional view of a SAW device. The device is positioned on a base comprising a glass-reinforced epoxy “FR4” layer (approximately 1.5mm thick), a polyethylene terephthalate (PET) layer (approximately 125pm thick), a nickel (Ni) layer (approximately 25pm thick) and a zinc Oxide (ZnO) (approximately 5pm thick). The IDT and the electrodes are positioned on the zinc oxide layer and typically comprise a conductor material such as chromium (C) approximately 50nm thicker gold (Au) approximately 120nm thick.

In certain embodiments, rather than providing a SAW device comprising an antenna pair, instead a single loop antenna is used.

Figure 6a provides a simplified schematic diagram of such an arrangement. In keeping with the device described with reference to Figure 1, the SAW device 601 shown in Figure 6 includes an interdigitated transducer (IDT) array 602 comprising a first and second set of interdigitated “fingers”, a first set of which are connected to a first electrode 603 and a second set of which are connected to a second electrode 604.

The SAW device 601 is substantially surrounded by a loop antenna 605.

The operation of the SAW device shown in Figure 6a corresponds to the operation of the SAW device described with reference to Figure 1, except that, as there is only one antenna in the arrangement shown in Figure 6, the resonant frequency of the SAW device cannot be detected by detecting a drop in the strength of the electromagnetic radiation received from the transmission antenna because there is only one antenna.

The loop antenna 605 is connected to a transmitter to transmit the electromagnetic energy but is also connected to a vector network analyser 606 (for example, via a first port, “Port 1” of the vector network analyser 606) used to detect the reflection parameter of the loop antenna. The reflection parameter can be measured by observing the “s11” spectrum at the vector network analyser or using an impedance analyser at the resonant frequency of the SAW device.

Advantageously, the arrangement shown in Figure 6a only requires a single antenna.

Similarly, in certain embodiments, as depicted schematically in Figure 6b, rather than using an oscillator and amplifier arrangement, the resonant frequency of the apparatus shown in Figure 1 can be determined by using a vector network analyser.

In certain embodiments, an array of SAW devices can be positioned between an antenna pair. Figure 7 provides a schematic diagram of such an arrangement.

The arrangement depicted in Figure 7 includes a first SAW device 701a and a second SAW device 701b, both the first SAW device 701a and the second SAW device 701b correspond to the SAW device described with reference to Figure 1. The first SAW device 701a and the second SAW device 701b are positioned between an antenna pair 702 comprising a transmission antenna 702a and a receiver antenna 702b.

In operation, if the geometries of the first SAW device 701a and the second 701b are different, two different resonant frequencies can be detected, i.e. as the frequency of the transmitted electromagnetic radiation is changed, the energy of the electromagnetic radiation received by the receiver antenna dips at two frequencies, one frequency corresponding to each SAW device. This is depicted in the graph shown in Figure 7. Advantageously, assuming that changes to the capacitance, Cidt, of each IDT don’t cause the resonant frequencies to overlap, such an arrangement can be used to characterise more than one medium from a single reading.

Figure 8 provides a schematic diagram of an apparatus in accordance with certain embodiments of the invention. The apparatus shown in Figure 8 corresponds to that shown in Figure 1 except that it further includes a power source 801 for providing electrical energy to the SAW device for actuating the medium.

For example, the power source can provide a suitable alternating current (AC) signal to the first electrode 103 and the second electrode 104 which causes actuation of any medium coupled to the IDT 102. With reference to Figure 3b, if such an AC signal was applied across the first electrode 303 and second electrode 304, fluid in the sample-holding cell 307 will be subject to mechanical actuation. Advantageously, in certain embodiments, this enables the medium to be characterised and actuated as part of the same process.

The AC signal can be generated by any suitable means. In certain embodiments this can be an AC signal generator coupled directly to the electrodes of the SAW device as shown in Figure 8. Alternatively, the AC signal could be wirelessly transmitted to the SAW device by electrically coupling suitable antennas to the electrodes and stimulating the antennas with an alternating electric field.

As described above, a medium can be characterised based on the change that it causes to Cidt when it is coupled to an IDT of a SAW device. In certain examples, as described above, the fluidic loading of a fluid can be characterised based on the capacitive coupling of the fluid with the IDT. Such embodiments of the invention can be used in applications such as biomolecular sensors, for example applications involving microfluidic processing. In such embodiments, the ability to actuate and characterise the medium in question may be particularly advantageous as typically in microfluidic processes actuation must be performed by separate actuation means.

Embodiments of the invention are not limited to characterising mediums such as fluids based on fluidic loading.

Other characteristics of a medium coupled to the IDT will cause a change to Cidt, for example where the medium is a gaseous, liquid or solid: conductivity, temperature; where the sample is a liquid or solid: gas absorption, and where the medium is a gaseous: humidity.

Such embodiments of the invention can be used in environmental monitoring applications. For example, with reference to Figure 3a, the IDT may be exposed to the air in a particular location and changes in the resonant frequency of the SAW device used to characterise the air by detecting the introduction into the location of undesirable substances such as toxic substances. Similarly, the air could be characterised by detecting changes in humidity.

It will be understood, that the characteristics of example mediums discussed above change Cidt principally by virtue of the medium being characterised capacitively coupling with the IDT of the SAW device. However, Cidt will also be subject to change if the geometry of the IDT is changed. In this way, in certain embodiments, the IDT can be physically coupled (either directly or via an intermediate element) to the medium being characterised to detect for example, changes brought about by physical changes such as mechanical bending, stretching, compressing, twisting and so on.

Such embodiments of the invention can be implemented in applications involving structural monitoring such as monitoring the development of defects is sensitive equipment such as pipes and conduits.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases at least one and one or more to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles a or an limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases one or more or at least one and indefinite articles such as a or an (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of two recitations, without other modifiers, means at least two recitations, or two or more recitations).

It will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope of the present disclosure. Accordingly, the 5 various embodiments disclosed herein are not intended to be limiting, with the true scope being indicated by the following claims.

Claims

1. A method of characterising a medium comprising:

stimulating with electromagnetic energy at least one electrical resonator device comprising an interdigitated transducer, said interdigitated transducer coupled with the medium;

detecting a frequency of the electromagnetic energy at which the electromagnetic energy establishes a circulating current within the electrical resonator device, said frequency dependent on a capacitance of the interdigitated transducer device, and characterising the medium based on the detected frequency.

2. A method according to claim 1, wherein stimulating the device with electromagnetic energy comprises emitting electromagnetic energy from a first antenna proximate the electrical resonator device.

3. A method according to claim 2, wherein the frequency of the electromagnetic energy at which the circulating current is established in the electrical resonator device is detected by detecting a change in the absorption of the electromagnetic energy by the electrical resonator device.

4. A method according to claim 3, further comprising receiving electromagnetic energy emitted from the first antenna at a second antenna proximate the interdigitated transducer device, and measuring an attenuation of the received electromagnetic energy emitted from the first antenna to detect the absorption of the electromagnetic energy by the interdigitated transducer.

5. A method according to claim 4, wherein the electrical resonator device is positioned substantially between the first antenna and second antenna.

6. A method according to any of claims 2 to 5, wherein the first antenna is coupled to an oscillator.

7. A method according to claim 3, wherein the first antenna is a loop antenna.

8. A method according to claim 5, wherein the loop antenna substantially encircles at least part of the electrical resonator device.

9. A method according to claim 8, further comprising measuring a reflection parameter of the electromagnetic radiation at the loop antenna to detect the absorption of the electromagnetic energy by the electrical resonator device and thereby determine the frequency at which the electromagnetic energy establishes the circulating current within the electrical resonator device.

10. A method according to any previous claim, further comprising stimulating with the electromagnetic energy one or more further electrical resonator devices each further electrical resonator device comprising a further interdigitated transducer each interdigitated transducer coupled with a further medium, detecting one or more further frequencies of the electromagnetic energy at which the electromagnetic energy establishes circulating currents within the one or more further electrical resonator devices, said one or more further frequencies dependent on a capacitance of the one or more further interdigitated transducer devices, and characterising the one or more further mediums based on the one further detected frequencies.

11. A method according to claim 10, wherein the frequency and the one or more further frequencies are detected substantially contemporaneously.

12. A method according to any previous claim, wherein the electrical resonator device comprises a surface acoustic wave (SAW) device.

13. A method according to claim 11, wherein the interdigitated transducer comprising a first set of fingers and a second set of fingers, said first and second set of fingers interdigitated with each other.

14. A method according to claim 13, wherein the surface acoustic wave device comprises a first electrode electrically coupled to the first set of fingers and a second electrode coupled to the second set of fingers.

15. A method according to claim 14, wherein the first electrode and second electrode are separated by a gap.

16. A method according to any of claims 12 to 15, further comprising applying electrical energy to the surface acoustic wave device to actuate the medium.

17. A method according to any previous claim, wherein the medium is a fluid.

18. A method according to claim 17, wherein the capacitance of the interdigitated transducer is dependent on a fluidic loading of the fluid on the interdigitated transducer.

19. An apparatus for characterising a medium, said apparatus comprising at least one electrical resonator device comprising an interdigitated transducer, said interdigitated transducer operable to be coupled to the medium to be characterised, wherein said apparatus further comprises an electromagnetic energy emitter operable to stimulate the electrical resonator device with electromagnetic energy and a detector operable to detect a frequency of the electromagnetic energy at which the electromagnetic energy establishes a circulating current within the electrical resonator device, said frequency dependent on a capacitance of the interdigitated transducer device, said detected frequency enabling the medium to be characterised.

20. An apparatus according to claim 19, wherein the electromagnetic energy emitter comprises a first antenna proximate to the electrical resonator device.

21. An apparatus according to any of claims 19 to 20, wherein the detector is arranged to establish the frequency of the electromagnetic energy at which the circulating current is established in the electrical resonator device is detected by detecting a change in the absorption of the electromagnetic energy by the electrical resonator device

22. An apparatus according to claim 21, wherein the detector comprises a second antenna proximate to the electrical resonator device operable to receive electromagnetic energy emitted from the first antenna, said detector comprising a signal analyser operable to measure an attenuation of the received electromagnetic energy emitted from the first antenna to detect the absorption of the electromagnetic energy by the interdigitated transducer.

23. An apparatus according to claim 22, wherein the electrical resonator device is positioned substantially between the first antenna and second antenna.

24. An apparatus according to claim 20 to 23, wherein the first antenna is coupled to an oscillator.

25. An apparatus according to claim 20, wherein the first antenna is a loop antenna.

26. An apparatus according to claim 25, wherein the loop antenna substantially encircles at least part of the electrical resonator device.

27. An apparatus according to claim 26, wherein the loop antenna is connected to a vector network analyser operable to measure a reflection parameter of the electromagnetic radiation at the loop antenna to detect the absorption of the electromagnetic energy by the electrical resonator device and thereby determine the frequency at which the electromagnetic energy establishes the circulating current within the electrical resonator device.

28. An apparatus according to any previous claim, said apparatus comprising at least one or more further electrical resonator devices comprising interdigitated transducers, the interdigitated transducers of the further electrical resonator device each operable to be coupled to further mediums to be characterised, wherein the electromagnetic energy emitter is operable to stimulate the one or more further electrical resonator devices with electromagnetic energy and the detector is operable to detect one or more further frequencies of the electromagnetic energy at which the electromagnetic energy establishes circulating currents within the one or more further electrical resonator devices, said one or more further frequencies dependent on a capacitance of the one or more interdigitated transducer device, said detected frequencies enabling the one or more further mediums to be characterised.

29. An apparatus according to claim 28, wherein the detector is operable to detect the one or more further frequencies substantially contemporaneously.

30. An apparatus according to any of claims 19 to 29, wherein the electrical resonator device comprises a surface acoustic wave (SAW) device.

31. An apparatus according to any of claims 19 to 30, wherein the interdigitated transducer comprising a first set of fingers and a second set of fingers, said first and second set of fingers interdigitated with each other.

32. An apparatus according to any of claims 19 to 31, wherein the surface acoustic wave device comprises a first electrode electrically coupled to the first set of fingers and a second electrode coupled to the second set of fingers.

33. An apparatus according to any of claims 19 to 32, wherein the first electrode and second electrode are separated by a gap.

34. An apparatus according to any of claims 29 to 33, comprising a power source for applying electrical energy to the surface acoustic wave device to actuate the medium.

35. An apparatus according to any of claims 19 to 34, wherein the medium is a fluid.

36. An apparatus according to claim 35, wherein the capacitance of the

5 interdigitated transducer is dependent on a fluidic loading of the fluid on the interdigitated transducer.

Intellectual

Property

Office

Application No:

GB1814829.6